1. Field of the Invention
The present invention relates to a zoom lens and an imaging apparatus suitably used in a small-sized apparatus having an imaging function, particularly, a video camera, a digital still camera, a portable telephone with a camera, and a personal digital assistance (PDA) or the like.
2. Description of Related Art
In recent years, in an imaging apparatus of a digital still camera or the like, in accordance with a progress of downsizing an imaging apparatus such as CCD. (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor). Further downsizing is requested for the apparatus as a whole. Hence, in recent times, there is developed a thin zoom lens when integrated to an imaging apparatus by constituting a so-to-speak bending-type optical system by bending an optical path of a lens system at a middle thereof.
As a zoom lens using a bending-type optical system, JP-A-2000-131610 and JP-A-2006-267862 each discloses a zoom lens of a four-group configuration including in order from the object side a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power and changing a magnification by moving the negative second lens group and the positive fourth lens group. Further, JP-A-2004-354869 discloses a zoom lens of a five-group configuration including in order from the object side a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power and changing a magnification by moving the negative second lens group and the positive fourth lens group. According to the zoom lenses described in these references, by arranging a prism at inside of the first lens group, an optical path is bended substantially by 90°. Further, there is disclosed an example constituted by a total of 3 lenses including one negative lens and a cemented lens having a second lens group.
As described above, by using the bending-type optical system, reducing the thickness of a zoom lens when integrated to an imaging apparatus can be achieved, and therefore, in recent years, the zoom lens is started to be mounted to various imaging apparatus. On the other hand, in the market there is also a request for being low in cost as well as reducing the thickness. Therefore, there is desired a development of a bending-type optical system having a constitution advantageous in view of cost while achieving reducing the thickness. In order to achieve reducing the thickness and being low in cost, it is conceivable to reduce a number of lenses by maintaining a performance in view of cost while achieving reducing the thickness. JP-A-2000-131610 discloses an example in which the second lens group includes 3 lenses, however, when the number of lenses can be further reduced.